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Additional Progress & Breakthroughs

The following are some of the major accomplishments of the USGCRP's Carbon Cycle Science Initiative during Fiscal Year 2000:

Net carbon uptake by terrestrial ecosystems was determined from the  AmeriFlux Network, which produces unique measurements of the net annual exchange of CO₂ between the atmosphere and terrestrial ecosystems. Data from 12 locations show that net carbon uptake is greater in warmer zones along the north-to-south climatic gradient from Canada to the southeastern United States. These observations are at variance with the conventional wisdom that more carbon accumulates at higher latitudes under colder temperatures. Scientists consider these carbon gains by the terrestrial biosphere significant.

Three ecosystem models simulating the impact of increasing CO₂ and climate on net carbon storage in U.S. terrestrial ecosystems -- and agreeing within 25 percent -- have yielded estimates of a land carbon sink that corresponds to about one-third of the estimated total carbon sink, based on inventory data. These model results suggest that other processes, such as regrowth on abandoned agricultural land or harvested forest lands, have larger effects on carbon storage and highlight the need for data on land-use history and more integrated modeling approaches. The model results also show evidence of significant year-to-year variability in carbon storage; variations of 100 percent from year to year are attributable to climate variability.

USGCRP agencies successfully implemented projects in Iowa and Montana to encourage changes in land management that should lead to increased carbon storage.

Long-term field experiments in which CO₂, water, and nutrients have been manipulated are producing unique data on ecosystem response to these global change variables. Results include increased vegetation growth, changes in water use, and increased carbon gain by several woody and herbaceous ecosystems. The observed decline in nitrogen content in plant tissues has implications for the quality of forage for animals that might graze in these systems, however.

A comprehensive synthesis effort is providing an inventory of carbon storage in the world's oceans that is based on observations. Previous estimates of the ocean sink had relied solely on model simulations. For example, the synthesis has revealed that more than 20 billion metric tons of excess atmospheric CO₂ are stored in the Indian Ocean. This effort represents an order of magnitude increase in the quantity and quality of carbon data obtained for the ocean as a result of improved analytical techniques and standards.